Tether assembly for a radio frequency controlled aircraft

ABSTRACT

A tether assembly for a radio-controlled model aircraft, including: a bracket arranged for fixed connection to the radio-controlled model aircraft and including a stop portion; and a bar with a first end pivotably connected to the bracket, and a second end arranged to connect to a flexible wire for a model aircraft anchoring system. Pivoting of the bar in a first rotational direction with respect to the bracket is limited by contact of the bar with the stop portion.

This application is a continuation-in-part patent application under 35USC 120 of U.S. patent application Ser. No. 13/250,103 filed Sep. 30,2011, which application is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates generally to a tether assembly for aradio-controlled model aircraft, in particular, a tether assembly for aradio-controlled model helicopter to prevent a guide wire from becomingentangled in the rotor for the helicopter.

BACKGROUND

Radio-controlled model helicopters are relatively difficult to controldue to the multiple degrees of freedom of movement possible for thehelicopter. Thus, it is difficult for a novice user to learn to fly amodel helicopter is an untethered state without causing erratic behaviorand uncontrolled movement of the helicopter. In fact, the learningprocess can result in damage to the helicopter. As a result, it isdesirable to provide a more controlled method of learning to fly a modelhelicopter. However, the prior art fails to teach a means by whichmovement of the helicopter can be restricted while enabling relativefreedom of movement of the helicopter.

SUMMARY

According to aspects illustrated herein, there is provided a tetherassembly for a radio-controlled model aircraft, including: a bracketarranged for fixed connection to the radio-controlled model aircraft andincluding a stop portion; and a bar with a first end pivotably connectedto the bracket, and a second end arranged to connect to a flexible wirefor a model aircraft anchoring system. Pivoting of the bar in a firstrotational direction with respect to the bracket is limited by contactof the bar with the stop portion.

According to aspects illustrated herein, there is provided aradio-controlled model helicopter, including: a fuselage; and a tetherassembly including: a bracket fixedly connected to the fuselage andincluding a stop portion; and a bar with a first end pivotably connectedto the bracket, and a second end arranged to connect to a flexible wirefor a model aircraft anchoring system. Rotation of the bar in a firstrotational direction with respect to the bracket is limited by contactof the bar with the stop surface.

According to aspects illustrated herein, there is provided a method ofoperating a radio-controlled model helicopter including a fuselage, arotor located at a top of the helicopter, and a tether assembly with abracket fixedly connected to the fuselage and with a bar with first endand a second end pivotably connected to the bracket, the bracketincluding a stop portion, including: connecting the first end to aflexible wire for a model aircraft anchoring system; displacing thehelicopter upward, against gravitational force, by rotating the rotor;pivoting the bar, with respect to the bracket, away from the rotor asthe helicopter displaces upward; displacing the helicopter downward;pivoting the bar, with respect to the bracket, toward the rotor;contacting the stop portion; and halting movement of the bar toward therotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prospective cut-away view of a radio-controlled modelairplane;

FIG. 2 is a representation of reference axes for an aircraft;

FIGS. 3A-C are details of a distal end of a wing for the airplane shownin FIG. 1;

FIG. 4 is a perspective view of a model airplane system;

FIG. 5 is a plan view of the model airplane system of FIG. 4 showing theairplane of FIG. 1 flying at a constant tangent;

FIG. 6 is a perspective view of the model airplane system of FIG. 4showing the airplane of FIG. 1 flying above the cap of the pylon;

FIG. 7 is a perspective view of the model airplane system of FIG. 4showing the airplane of FIG. 1 performing a figure 8;

FIG. 8 is a perspective view of a model helicopter with a tetherassembly;

FIG. 9 is a perspective bottom view of the tether assembly shown in FIG.8;

FIG. 10 is a perspective top bottom view of the tether assembly shown inFIG. 8;

FIG. 11 is an exploded view of the tether assembly shown in FIG. 8;

FIG. 12 is a detail of a stop surface for a tether assembly; and,

FIGS. 13A through 13D are pictorial representations of aradio-controlled model helicopter with a tether assembly.

DETAILED DESCRIPTION

At the outset, it should be appreciated that like drawing numbers ondifferent drawing views identify identical, or functionally similar,structural elements of the invention. While the present invention isdescribed with respect to what is presently considered to be thepreferred aspects, it is to be understood that the invention as claimedis not limited to the disclosed aspects.

Furthermore, it is understood that this invention is not limited to theparticular methodology, materials and modifications described and assuch may, of course, vary. It is also understood that the terminologyused herein is for the purpose of describing particular aspects only,and is not intended to limit the scope of the present invention, whichis limited only by the appended claims.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this invention belongs. Although any methods, devicesor materials similar or equivalent to those described herein can be usedin the practice or testing of the invention, the preferred methods,devices, and materials are now described.

FIG. 1 is a prospective cut-away view of a radio-controlled modelairplane, or aircraft, 100. In the description that follows, the termsairplane and aircraft are used interchangeably. Airplane 100 includesfuselage 102, horizontal stabilizer 104 with controllable rear elevator106 connected, for example, hingedly connected, to the horizontalstabilizer, and wings 108 and 110 including controllable flaps 112 and114 connected, for example, hingedly connected, to the first and secondwings, respectively. The airplane also includes tail fin 115 and controlsystem 116 including battery 118, and receiver 120 powered by thebattery and arranged to receive radio frequency signals from atransmitter (not shown), and computer 124 powered by the battery,electrically connected to the receiver, and arranged to transmit controlsignals in response to the received radio frequency signals. In anexample embodiment, the receiver operates at 2.4 GHz; however, it shouldbe understood that other frequencies are possible. In an exampleembodiment, the receiver and computer are on single electronic board125; however, it should be understood that other configurations arepossible. Motor 126 is powered by the battery and arranged to receivethe transmitted control signals to rotate propeller 128. That is, thepropeller provides the force to launch and sustain the airplane inflight according to signals received by the receiver and transmitted bythe computer.

Aircraft 100 is not restricted to any particular configuration or shape,except as needed to implement the configurations and functions describedbelow. Receiver 120 and computer 124 can be any receiver and computerknown in the art. In an example embodiment, computer 124 is amicroprocessor. Motor 126 can be any motor known in the art. Receiver120 can receive signals from any radio frequency transmitter known inthe art. The battery can be any battery known in the art, for example,including, but not limited to, a rechargeable and replaceable LiPObattery of 3.7 volts with a capacity of 150 MAH

In an example embodiment, the airplane includes motor 128 powered by thebattery and arranged to receive the transmitted control signals toswivel elevator 106 or flaps 112 and 114. For example, motor 128 isarranged to perform the following operations:

1. Swivel, with respect to a same frame of reference (indicated by arrow129), flaps 112 and 114 in clockwise direction CD and to swivel the rearelevator in counter clockwise direction CCD; or,

2. Swivel, with respect to the same frame of reference, flaps 112 and114 in direction CCD and the rear elevator in the direction CD.

Thus, using a single motor 128 and a linkage system described below,computer 124 is able to control flaps 112 and 114 and flaps 106simultaneously. Motor 128 can be any motor known in the art. In anexample embodiment, motor 128 is a servo-motor.

In an example embodiment, the tail fin includes rudder 130 which isfixed with respect to the tail fin. For example, the rudder is in a“zero” position of maximum alignment with the tail fin, or the rudder isat a fixed angle with respect to the tail fin, for example, to maintaintension on the guide wire noted below. In an example embodiment, rudder130 is displaceable, for example, the rudder is hingedly connected tothe tail fin, and the airplane includes motor 132 powered by the batteryand arranged to receive the transmitted control signals. Motor 132 isarranged to swivel the rudder in response to the control signals fromthe computer. Motor 132 can be any motor known in the art. In an exampleembodiment, motor 132 is a servo-motor. In an example embodiment, thecomputer is arranged to transmit the control signals to simultaneouslycontrol motors 128 and 132.

Airplane 100 includes single flexible wire 134 passing through opening136 at distal end 138 of one of the wings, for example, the wingpointing inward as the plane traverses a circular path. As shown in thefigures, airplane 100 is oriented to fly in a counterclockwise direction(looking down from above the airplane); therefore, opening 136 islocated on wing 108. If airplane 100 is oriented to fly in a clockwisedirection (looking down from above the airplane); opening 136 is locatedon wing 110. End 140 of the wire is fastened to point 142 at or near ajunction of the fuselage and the wing, for example, wing 108, upon whichopening 136 is located. In an example embodiment, the wire passesthrough an internal space in the wing from opening 136 to point 142.Second end 144 of the wire, not shown in FIG. 1, but shown in FIG. 4below, is arranged for connection to a point outside of the modelairplane. The single flexible wire is used solely to guide the airplaneand restrain the airplane to a circular flight path as further describedbelow. However, the flexibility of the wire enables the airplane to flywithin the circular flight path as further described below. The wire isnot used to transmit power or control signals to the model airplane.

FIG. 2 is a representation of reference axes for aircraft AP. It shouldbe understood that the location of the axes in FIG. 2 is substantiallyapplicable to airplane 100. Longitudinal axis LOA passes throughfuselage F of airplane AP, substantially from tail to nose. “Roll” ismovement or rotation about LOA. Lateral axis LAA passes through wings Wand fuselage F and is perpendicular to LOA. “Pitch” is movement orrotation about LAA. Vertical axis VA passes through F and isperpendicular to LOA and LAA. “Yaw” is movement or rotation about VA. Asin known in the art, the exact locations and intersects of the axesdepends on the specifics of a particular airplane, for example, theconfiguration and propulsion system of the airplane.

The following should be viewed in light of FIGS. 1 and 2.Advantageously, the presence of wire 134 and the positioning of opening136 and point 142 enable desirable stability of airplane 100 while inflight, combined with optimal sensitivity to control commands. In anexample embodiment, the location of point 142 is selected throughcareful analysis of the structure, configuration, and flightcharacteristics of airplane 100 such that when flaps 112 and 114 are ata position of greatest alignment with wings 108 and 110, respectively,and flaps 106 are at positions of greatest alignment with the horizontalstabilizer, the model airplane is arranged to fly with LOA horizontal.That is, airplane 100 flies in a steady horizontal plane without“pitch.” The respective positions of greatest alignment described abovefor flaps 112 and 114 and flaps 106 are referred to as “zero positions”in the art. For example, swiveling the flaps out of the zero positionscauses some type of pitch. Without the careful placing of point 142undesirable pitch occurs. For example, if point 142 is too close to nose146 of airplane 100, the nose pitches downward and if point 142 is tooclose to tail 148 of airplane 100, the nose pitches upward.

As further described below, wire 134 has a length defining a circularflight path for the model airplane. In an example embodiment, thelocation of opening 136, in particular with respect to LOA, is selectedthrough careful analysis of the structure, configuration, and flightcharacteristics of airplane 100 such that when the rudder is in aposition of greatest alignment with the tail fin, the model airplane isarranged to fly at a constant tangent with respect to the circular path.That is, airplane 100 flies without undesirable yaw. For example, nose146 does not point too far inward of the circular path or too faroutward of the circular path. The position of greatest alignmentdescribed above for the rudder is referred to as “zero position” in theart. For example, swiveling the rudder out of the zero positions causesyaw. Without the careful placing of opening 136 undesirable yaw occurs.For example, if point 142 is too close to nose 146 of the airplane, thenose yaws inward of the flight path and if opening 136 is too close totail 148 of the airplane, the nose yaws outward of the flight path.

The location of point 142 influences the handling characteristics ofairplane 100. For example, is point 142 is too close to nose 146 theresponse of airplane 100 to control is undesirably sluggish, and ifpoint 142 is too close to tail 148 the response of airplane 100 tocontrol is undesirably sensitive and unstable.

Airplane 100 includes linkage system 150 connecting motors 128 and 132to flaps 106 and flaps 112 and 114, and the rudder, respectively. In anexample embodiment, system 150 includes pushrod 152 connected to motor128 and control horn 154 in order to actuate the swiveling of flaps 112and 114. Control horn 154 transmits this motion through pushrod 156 tocontrol horn 158 connected to flaps 106. Thus, the linkage systemenables the synchronized motion of flaps 112 and 114 and elevator 106noted above. Thus, motor 128 provides a linear movement through pushrods152 and 156 to control horns 154 and 158 in order to move flaps 112 and114 and elevator 106 in tandem. Therefore, a single motor is used toexecute two mechanical commands (flaps 112 and 114 and elevator 106,respectively), eliminating the need for a second motor, whichadvantageously reduces the weight of aircraft 100. The reduction inweight increases performance, and provides the operator with moreprecise control of aircraft 100. Via the aerodynamic principle of movingflaps 112 and 114 and elevator 106 in unison and in opposite directions,the aircraft is able to optimally create moment and lift at the sametime allowing the operator of the model aircraft to generate sharperturns (corners) and loops which in turn allows for better performanceindoors and in smaller space environments.

In an example embodiment, system 150 includes pushrod 160 connected tomotor 132 and control horn 162 in order to actuate the swiveling of therudder. It should be understood that system 150 is not limited to thecomponents and configuration shown and that other components andconfigurations are possible.

FIGS. 3A-C are details of a distal end of a wing for airplane 100. Thepresence of the wire in wing 108 or wing 110 also enables desirableflight characteristics and a desirable flight path for airplane 100. Thefollowing description is with respect to wing 108; however, it should beunderstood that the description also is applicable to wing 110. Ingeneral, as airplane 100 flies in the circular path noted above and wire100 is substantially taut, forces exerted by the wire, in particular atdistal end 138, urge wing 108 upward or downward such that end 140 ofthe wire, opening 136, and the other end of the wire are in a straightline, that is, are aligned, as shown in FIG. 3A. If end 138 rolls upwardtoo far, as shown in FIG. 3B, bottom edge 164 of opening 136 contactsthe wire and exerts force F1 on the wire so that the ends of the wireare no longer aligned through opening 136. However, the wire reacts toF1 with opposite force F2, pushing end 138 down so that theconfiguration shown in FIG. 3A is attained. If end 138 rolls downwardtoo far, as shown in FIG. 3C, top edge 166 of opening 136 contacts thewire and exerts force F3 on the wire so that the ends of the wire are nolonger aligned through opening 136. However, the wire reacts to F3 withopposite force F4, pushing end 138 up so that the configuration shown inFIG. 3A is attained. Thus, wire 134 provides automatic stabilizationwith respect to roll about LOA. The operation of wire 134 is furtherdescribed below.

FIG. 4 is a perspective view of model airplane system 200. Modelairplane system 200 includes anchoring system 202 and airplane 100.System 200 is shown with a single airplane 100; however, it should beunderstood that system is not limited to a single airplane 100 and thata plurality of airplanes 100 can be used in system 200. Further, itshould be understood that if a plurality of airplanes 100 are used insystem 200, different types of airplanes 100 can be used. By differenttypes of airplanes 100 we mean that the shape and configurations of theairplanes can vary as long as the airplanes include the applicablestructure and function described above and below for airplane 100.System 202 includes base 204, pylon 206 fixedly secured to the base, cap208 at distal end 210 of the pylon, and ring 212 disposed about thepylon, rotatable about the pylon, and displaceable along a length of thepylon. That is, ring 212 fits loosely enough about the pylon such thatthe ring can rotate around the pylon and be moved up and down along thepylon in direction AD. Base 204 can be a hollow reservoir base to befilled with water, sand or gravel in order to add weight to stabilizethe centrifugal force created by the aircraft, and the pylon can befixed in the middle of the base. The pylon can be made of multiplesegments to allow for height adjustment. The ring or rings fit looselyabout the pylon to allow the aircrafts to fly around the pylon atvariable speeds. Since the rings slide vertically, the rings adaptthemselves to the desired altitude of the aircraft as the operatorcontrols the aircraft via flaps 106 and flaps 112 and 114. The cable isthin and flexible and has any desired length in order to fit enclosedindoor spaces or outdoors. The only function of the cable is to tetherthe aircraft to the ring and pylon.

End 144 of wire 134 is fixedly connected to the ring. The cap preventsthe ring from displacing past the distal end, that is, the ring cannotslide over the cap. Any base, pylon, cap, or ring known in the art canbe used. It should be understood that other configurations are possible,with the general understanding that a ring is rotatable about andaxially displaceable along a fixed element such as a pylon that issecurely anchored. As described above, end 140 of the wire is connectedto point 142 in airplane 100.

As noted above, the location of point 142 is selected through carefulanalysis of the structure, configuration, and flight characteristics ofairplane 100 such that when flaps 112 and 114 are at a position ofgreatest alignment with wings 108 and 110, respectively, and elevator106 are at a position of greatest alignment with the horizontalstabilizer, the model airplane is arranged to fly with LOA horizontal.In portion 214A of the circular flight path, airplane 100 is flying withLOA horizontal.

FIG. 5 is a plan view of system 200 showing airplane 100 flying at aconstant tangent. The following should be viewed in light of FIGS. 1through 5. As noted above, wire 134 has length L defining circularflight path 214 for the model airplane. L is not restricted to anyparticular value. L can be relatively short, for example, 8 feet, toenable use of system 200 within a room or L can be longer for use ofsystem 200 outdoors. As noted above, the location of opening 136, inparticular with respect to LOA, is selected through careful analysis ofthe structure, configuration, and flight characteristics of airplane 100such that when the rudder is in a position of greatest alignment withthe tail fin, the model airplane is arranged to fly at constant tangentCT with respect to the circular path. That is, angle TA between CT and214 remains constant and airplane 100 flies without undesirable yaw. Theoperation of airplane 100 in FIG. 5 can be explained as follows. Theairplane flies in direction CCD and force DF acts to keep the airplanemoving in direction CCD. Centrifugal force 216 pushes the plane outwardand centripetal force 218 pulls the plane inward (with respect to thepylon). The key to the stability and the ability of the airplane tomaintain the constant tangent is tension force TF generated by the wirein reaction to the direction force. When point 144 is properly selected,the combination of forces results in the airplane maintaining theconstant tangent.

If the guide wire does not pass through the wing and is only attached tothe fuselage, undesirable yaw of the nose occurs, for example, inward oroutward of the flight path. As a result, the airplane assumes anundesirable orientation, for example, LOA of the airplane crosses thecircular flight path (the nose points more toward or more away from acenter point for the circular path) rather than being tangential to thecircular flight path. If opening 136 is improperly placed undesirableyaw also occurs, for example, if the opening is too close to tail 148 ofthe airplane, the nose yaws outward of the flight path.

The use of a single flexible guide wire in conjunction with thepositioning of the guide wire and the controllability of elevator 106,flaps 112 and 114, and the rudder enable a wide-ranging and complex setof maneuvers for airplane 100. For example, returning to FIG. 4, theairplane is shown performing an internal loop. In this case, elevator106 and flaps 114 and 114 are swiveled to enable the loop and the guidewire and the positioning of the guide wire enable the airplane to remainstable during the loop.

FIG. 6 is a perspective view of model airplane system 200 showingairplane 100 flying above the cap on the pylon. The use of a singleflexible guide wire in conjunction with the positioning of the guidewire and the controllability of elevator 106, flaps 112 and 114, and therudder also enable the airplane to fly above the cap. This capabilityincreases the vertical maneuvers possible in system 200. Approximatesequential positions of wire 134 in the sequence of FIG. 6 are shown bynumerals 134A-E.

FIG. 7 is a perspective view of model airplane system 200 showingairplane of 100 performing a figure 8. Since guide wire 134 is flexible,airplane 100 is able to fly within circular flight path 214. Forexample, the rudder can be used to move the airplane inward of path 214.Thus, as shown in FIG. 8 a complicated figure 8 pattern, which requiresthe airplane to fly above the cap, perform loops, and fly inward of path214 is accomplished. To clarify the view of FIG. 8, the guide wire hasnot been shown.

Thus, airplane 100 is a totally wirelessly radio controlled tetheredmodel scale airplane able to take off, land, climb, accelerate, dive,perform loops, vertical flight, knife flight, Cuban eight, stalls,inverted flight, flips, regular eight, square loops, and many threedimensional flight maneuvers while the operator is situated remotelyoutside the flight circumference. The preceding motion occurs withinflight paths that are prescribed in an outward direction by flight path214 and length L of the wire which form a dome-capped right anglecylinder. However, as noted above, for example, as shown in FIG. 8,flight within the cylinder is possible.

In general, the centrifugal force created by the airplane will tend totense the guide wire as this force urges the airplane away from thepylon. However, through the use of the controllable rudder, the airplanealso can fly inside the circumference of the cylinder.

In an example embodiment, the RPM of motor 126 are regulated byelectronic speed control (ESC) 154, which is also located in theaircraft, for example, associated with computer 124. This arrangementenables the operator to regulate the speed of the aircraft. Toaccomplish this control wirelessly, the aircraft used the radiofrequency control signals noted above. Computer 124 transmits controlsignals to the ESC that open or close the throttle of motor 126 toregulate the speed of airplane 100 and converts the radio frequencycontrol signals into an electronic signal in order to command motors 128and 132 which in turn convert these electronic commands into linealmechanical commands to actuate elevator 106, flaps 112 and 114, and therudder.

FIG. 8 is a perspective view of a model helicopter with tether assembly300.

FIG. 9 is a perspective bottom view of tether assembly 300 shown in FIG.8.

FIG. 10 is a perspective top view of tether assembly 300 shown in FIG.8.

FIG. 11 is an exploded view of tether assembly 300 shown in FIG. 8. Thefollowing should be viewed in light of FIG. 8 through 11. Tetherassembly 300 includes bracket 302 arranged for fixed connection to theradio-controlled model aircraft, for example, model helicopter 304. Theassembly also includes stop portion 306 and bar 308 with end 310pivotably connected to the bracket and end 312 arranged to connect to aflexible wire for a model aircraft anchoring system. As furtherdescribed below, pivoting of the bar in rotational direction RD1 withrespect to the bracket is limited by contact of the bar with the stopportion. Although bar 308 is shown in three portions in FIG. 11, itshould be understood that the bar could have more than three portions orfewer than three portions.

In an example embodiment, the bracket includes at least one attachmentportion 314 arranged for fixed connection to an aircraft, and side walls316 and 318 extending from portion 314. The stop portion is disposedbetween and connected to the walls, and end 310 is disposed between theside walls. In an example embodiment, the stop portion includes stopsurface 320 with indent 322 arranged to matingly engage end 310. Forexample, the curve of the indent matches the curve of the outsidesurface 324 of the bar.

In an example embodiment, the assembly includes pin 326, end 310includes slot 328 at least partially formed by distal end 330 of the barand including opening 332 facing away from the stop portion when the baris in contact with the stop portion. The pin passes through the slot,and the bar is pivotable about the pin. In an example embodiment, thebar is removable from the bracket by pivoting the bar away from the stopportion, that is, pivoting the bar in direction RD2, opposite RD1, suchthat opening 332 faces the bracket and the bar can be displaced indirection AD away from the pin.

In an example embodiment, the bracket includes attachment surface 334arranged to contact an aircraft, and when the bar is in contact with thestop portion, longitudinal axis LA for the bar is about orthogonal tothe attachment surface. That is, the bar extends away from a side of theaircraft. In an example embodiment, the attachment portion includesattachment surface 334 arranged to contact the radio-controlled modelaircraft, and stop surface 320 is orthogonal to the attachment surface.

FIG. 12 is a detail of a stop surface for a tether assembly. In anexample embodiment, stop surface 320 is orthogonal to the side walls,that is, the stop surface is flat instead of curved.

In an example embodiment, radio-controlled model aircraft 304 is a modelhelicopter including fuselage 336 to which the tether assembly issecured. In an example embodiment, the tether assembly is directlyfixedly connected to the fuselage. The helicopter includes landingassembly 338 connected to bottom 340 of the helicopter, and rotatablerotor 342 with blades 343 at top 344 of the helicopter. Direction RD1 isfrom bottom 340 toward top 344. The rotor includes axis of rotation AR.In an example embodiment, when the bar is in contact with the stopsurface, the bar is about orthogonal to the axis of rotation. Ingeneral, the stop portion limits movement of the bar toward the rotor,for example, to prevent the flexible line from contacting therotor/blades. In an example embodiment, the bar has a pivoting range ofmotion of at least 90 degrees with respect to the bracket. In an exampleembodiment, the bar has a pivoting range of motion of no more than 90degrees with respect to the bracket.

FIGS. 13A through 13D are pictorial representations of radio-controlledmodel helicopter 304 with tether assembly 300. The following should beviewed in light of FIGS. 8 through 13D. The following describes apresent invention method for operating a radio-controlled modelhelicopter. Although the method is presented as a sequence of steps forclarity, no order should be inferred from the sequence unless explicitlystated. An example of the use of a radio-controlled model helicopterwith assembly 300 is shown in FIGS. 13A through 13D. In an exampleembodiment, the radio-controlled model helicopter is helicopter 304including fuselage 336, rotor 342, and tether assembly 300. A first stepconnects end 310 to a flexible wire for a model aircraft anchoringsystem, for example, wire 134 for system 200, as shown in FIG. 13A. Inthis position, bar 308 can be orthogonal to AR; however, the bar couldbe rotated further in direction RD2 than shown in FIG. 12A, that is, thebar may not be in contact with surface 320.

A second step displaces the helicopter upward, against gravitationalforce, by rotating the rotor, as shown in FIG. 13B. A third step pivotsthe bar, with respect to the bracket, away from the rotor as thehelicopter displaces upward, also as shown in FIG. 13B. That is, the barpivots in direction RD2. In FIG. 13B, the bar has rotated as far aspossible in direction RD2. It should be understood that the amount ofrotation of the bar in direction RD2 is at least partially a function ofthe shape of the helicopter and fuselage, which the bar may contact toprevent further rotation in direction RD2. A fourth step displaces thehelicopter downward, as shown in FIG. 13C. A fifth step pivots the bar,with respect to the bracket, toward the rotor, that is, in directionRD1, also as shown in FIG. 13C. A sixth step continues to displace thehelicopter downward such that bar 308 rotates further in direction RD1to contact the stop portion with the bar, as shown in FIG. 13D. Aseventh step halts movement of the bar toward the rotor, also as shownin FIG. 13D. It should be understood that during the course of operatingthe helicopter, the orientation of the bar can vary between thepositions shown in FIGS. 13A and 13B. For example, the helicopter canrise with the bar in contact with the stop portion.

In general, halting movement of the bar toward the rotor/blades includeshalting movement of the flexible wire toward the rotor/blades. Statedotherwise, halting movement of the bar toward the rotor\blades includespreventing the flexible wire from contacting the rotor\blades andbecoming entangled with the rotor\blades.

As noted above, learning to fly a radio-controlled model helicopter inan untethered state can be difficult, resulting in frustration for thelearner and damage to the helicopter. Advantageously, assembly 300enables the helicopter to be connected to a tethering system, such assystem 200, while ensuring that a tether line or wire, such as wire 134,does not become entangled in the rotor\blades of the helicopter. At thesame time, assembly 300 enables a large degree of freedom of movementfor the helicopter. For example, the helicopter is able to take off, flyupwards and downwards, and land virtually unhindered by the assembly, asshown in FIGS. 13A through 13D. For example, when the helicopter isconnected to wire 134 and system 200, as the helicopter descents, thebar contacts the stop portion, locking any further rotation of the bartoward the rotor. As a result, the bar causes the slip ring to descendin unison with the bar. Without the bar, the helicopter would descend,the slip ring could remain fixed, or descend at a lesser rate, and thewire would contact the rotor\blades.

Thus, it is seen that the objects of the invention are efficientlyobtained, although changes and modifications to the invention should bereadily apparent to those having ordinary skill in the art, withoutdeparting from the spirit or scope of the invention as claimed. Althoughthe invention is described by reference to a specific preferredembodiment, it is clear that variations can be made without departingfrom the scope or spirit of the invention as claimed.

What is claimed is:
 1. A tether assembly for a radio-controlled modelaircraft, comprising: a bracket arranged for fixed connection to theradio-controlled model aircraft and including a stop portion; and, a barwith: a first end pivotably connected to the bracket; and, a second endarranged to connect to a flexible wire for a model aircraft anchoringsystem, wherein: pivoting of the bar in a first rotational directionwith respect to the bracket is limited by contact of the bar with thestop portion.
 2. The tether assembly of claim 1, wherein: the bracketincludes: at least one attachment portion arranged for fixed connectionto the radio-controlled model aircraft; and, first and second side wallsextending from the at least one attachment portion; the stop portion isdisposed between and connected to the first and second side walls; and,the first end is disposed between the first and second side walls. 3.The tether assembly of claim 2, wherein: the first and second side wallsare parallel to each other; and, the stop portion includes a stopsurface orthogonal to the first and second side walls.
 4. The tetherassembly of claim 2, wherein the stop portion includes a stop surfacewith an indent arranged to matingly engage the first end.
 5. The tetherassembly of claim 1, further comprising a pin, wherein: the first endincludes a slot at least partially formed by a first distal end of thebar and including an opening facing away from the stop portion when thebar is in contact with the stop portion; the pin passes through theslot; and, the bar is pivotable about the pin.
 6. The tether assembly ofclaim 5, wherein the bar is removable from the bracket by pivoting thebar away from the stop portion.
 7. The tether assembly of claim 1,wherein: the bracket includes an attachment surface arranged to contactthe radio-controlled model aircraft; and, when the bar is in contactwith the stop portion, a longitudinal axis for the bar is aboutorthogonal to the attachment surface.
 8. The tether assembly of claim 1,wherein: the attachment portion includes an attachment surface arrangedto contact the radio-controlled model aircraft; and, the stop portionincludes a stop surface: arranged to contact the bar; and, orthogonal tothe attachment surface.
 9. A radio-controlled model helicopter,comprising: a fuselage; and, a tether assembly including: a bracketfixedly connected to the fuselage and including a stop portion; and, abar with: a first end pivotably connected to the bracket; and, a secondend arranged to connect to a flexible wire for a model aircraftanchoring system, wherein: rotation of the bar in a first rotationaldirection with respect to the bracket is limited by contact of the barwith the stop surface.
 10. The radio-controlled model helicopter ofclaim 9, wherein the tether assembly is directly connected to thefuselage.
 11. The radio-controlled model helicopter of claim 9, wherein:the helicopter includes: a landing assembly connected to a bottom of thehelicopter; and, a rotatable rotor at a top of the helicopter; and, thefirst rotational direction is from the bottom toward the top.
 12. Theradio-controlled model helicopter of claim 9, wherein: the helicopterincludes a rotatable rotor at a top of the helicopter; the rotorincludes an axis of rotation; and, when the bar is in contact with thestop surface, the bar is about orthogonal to the axis of rotation. 13.The radio-controlled model helicopter of claim 9, wherein: thehelicopter includes a rotatable rotor at a top of the helicopter; and,the stop portion limits movement of the bar toward the rotor.
 14. Theradio-controlled model helicopter of claim 9, wherein: the bracketincludes: at least one attachment portion arranged for fixed connectionto the radio-controlled model aircraft; and, first and second side wallsextending from the at least one attachment portion; the stop surface isdisposed between and connected to the first and second side walls; and,the first end is disposed between the first and second side walls. 15.The radio-controlled model helicopter of claim 9, wherein the bar has apivoting range of motion of at least 90 degrees with respect to thebracket.
 16. The radio-controlled model helicopter of claim 9, whereinthe bar has a pivoting range of motion of no more than 90 degrees withrespect to the bracket.
 17. A method of operating a radio-controlledmodel helicopter including a fuselage, a rotor located at a top of thehelicopter, and a tether assembly with a bracket fixedly connected tothe fuselage and with a bar with first end and a second end pivotablyconnected to the bracket, the bracket including a stop portion,comprising: connecting the first end to a flexible wire for a modelaircraft anchoring system; displacing the helicopter upward, againstgravitational force, by rotating the rotor; pivoting the bar, withrespect to the bracket, away from the rotor as the helicopter displacesupward; displacing the helicopter downward; pivoting the bar, withrespect to the bracket, toward the rotor; contacting the stop portion;and, halting movement of the bar toward the rotor.
 18. The method ofclaim 17 wherein halting movement of the bar toward the rotor includeshalting movement of the flexible wire toward the rotor.
 19. The methodof claim 17 wherein halting movement of the bar toward the rotorincludes preventing the flexible wire from contacting the rotor.